1. Field of the Invention
The present invention relates to a method for impregnating a resin-absorbable tubular liner with resin, which is performed as a step in the manufacturing of a tubular liner assembly to be used in lining of a tubular conduit.
2. Description of the Prior Art
When an underground pipe, such as pipelines and passageways, becomes defective or too old to perform properly, the pipe is repaired and rehabilitated without digging the earth to expose the pipe and disassembling the sections of the pipe. This non-digging method of repairing an underground pipe has been known and practiced commonly in the field of civil engineering. Typically, the method is disclosed by Japanese Provisional Patent Publication (Kokai) No. 60-242038.
According to this publication, this method of pipe mending comprises inserting a sufficiently long tubular flexible liner bag into the pipe to be repaired by means of a pressurized fluid, such as air and water. The tubular liner bag is made of a flexible resin-absorbable cloth material impregnated with a thermosetting (heat-curable) liquid resin, and has the outer surface covered with an impermeable plastic film.
More particularly, according to the publication, the tubular flexible liner bag is very long and closed at one end and open at the other. The tubular flexible liner bag is first flattened, then, the open end of it is made to gape wide and hooked (anchored) at one end of the defective or old pipe in a manner such that the wide-opened end of the liner bag completely and fixedly covers and closes the pipe end; a portion of the liner bag is pushed into the pipe whereby an annular pocket is made; then, a pressurized fluid is applied to the pocket portion of the tubular liner bag such that the fluid urges the tubular liner bag to enter the pipe. Since one end of the tubular liner bag is hooked at the end of the pipe, it remains there while the rest of the flexible liner bag proceeds deeper in the pipe as it is turned inside out. (Hereinafter, this manner of insertion shall be called "everting" or "eversion".) When the entire length of the tubular liner bag is everted (i.e., turned inside out) into the pipe, the everted tubular liner bag is pressed against the inner wall of the pipe by the pressurized fluid or by an inflatable pressure bag later introduced into the pipe, and the tubular flexible liner bag is hardened as the thermosetting liquid resin impregnated through the thickness of the liner bag is heated, which is effected by heating the pressurized fluid filling the tubular liner bag by means of a hot steam, etc. Thereafter the closed end of the liner bag is cut off. It is thus possible to line the inside wall of the defective or old pipe with a rigid liner without digging the ground and disassembling the pipe sections.
Now, in manufacturing a tubular liner assembly to be used in such a pipe lining method as described above, the resin-absorbable tubular liner made from a nonwoven fabric, whose outer surface is air-tightly covered with a polymeric film, is soaked with an uncured curable liquid resin such as unsaturated polyester resin; and as a method for effecting this soaking of the resin-absorbable tubular liner with the resin, there is proposed a procedure as disclosed in U.S. Pat. No. 4,366,012.
According to this patent: a required amount of hardenable (curable) resin is injected into the hollow of the resin-absorbable tubular liner; and a window is made open through the film covering the outer surface of the resin-absorbable tubular liner; and the air is drawn out of the resin-absorbable tubular liner through this window while the resin-absorbable tubular liner is passed between a pair of squeeze means to thereby push the hardenable resin toward the window, which promotes progressive soaking of the resin-absorbable tubular liner with the hardenable resin; then, when the advancing resin nears the window, the window is closed by means of patches, etc., and a new window is made open at a location downstream to the closed window, and the same operation as described above is repeated. This repetition is continued until the entire length of the resin-absorbable tubular liner is soaked with the hardenable liquid resin.